1. Field of the Invention
The present invention relates to a non-volatile counter, and more precisely, relates to a non-volatile counter in which data is stored in erasable and writable semiconductor non-volatile memory devices.
2. Description of the Related Art
A non-volatile counter in which a counter circuit for counting pulses and a non-volatile memory device such as EEPROM or the like are arranged in parallel to each other, wherein when the value of the counter is changed that value is written in the EEPROM, is well known.
The non-volatile counter can be used as an electronic trip meter of a car or a data collecting device in a plant or the like as it can hold data in the memory after the electric power supply thereto is shut off.
The non-volatile counter provided with the non-volatile memory device such as EEPROM or the like, however, has a problem in that a maximum counting value to be counted is necessarily restricted to a certain value, due to a limitation of the number erasing and writing operations of the EEPROM. Note, since the EEPROM has an endurance characteristic, the number of the erasing and writing operations thereof is naturally limited; for example, when a binary counter is used, the number of changes of data is largest in the least significant bit (LSB), and thus the upper limit of the counting value is inherently decided by the capacity to change the number of data per unit time in the least significant bit (LSB).
Further, when a deficit arises in a memory cell and when the bit in which the deficit arises is a higher digit, the data obtained therefrom is completely different to the correct data.
To overcome these problems, a counter in which a plurality of memory cells for memorizing the count value, especially in a lower digit, is provided in the EEPROM, and the count values for the lower digit are sequentially written in one of the memory cells in turn, to thereby improve the upper limitation of the count value, has been proposed, or a counter in which the same counted values are stored in a plurality of the memory cells and one data thereof is selected therefrom by applying a majority logic thereto, to thereby improve a reliability thereof, also has been proposed.
Even when these counters are used, however, the problems above are not necessarily completely resolved.
Note, when these counters are used, other problems arise in that the number of the cells is naturally increased, and moreover, a monitoring operation for checking a number of writing operations of the memory cells or an operation for processing a majority logic to check the reliability of the cells, must be carried out separately.
Further, when performing these operations, a micro-computer for controlling these operations is usually required, to thereby make the construction of the cells complicated, and accordingly, the reliability thereof will be lost.
Further, in this case, when the micro-computer malfunctions, it becomes difficult to read the count value.
Therefore, to overcome these problems, the present invention provides a non-volatile counter having a simple construction which can improve the upper limitation for the counting value, and further, improve the reliability of the memorized counting value.
To attain the above object of the present invention, there is provided a non-volatile counter which updates data stored in erasable and writable non-volatile memory devices based on count data and performs a counting operation, said memory devices being arranged as an array of cells having a predetermined number of bits, wherein said counter is provided with a selecting means for selecting a cell corresponding to a value of a predetermined digit of said count from said cell array and a writing means for writing data corresponding to the value of a digit different from said predetermined digit in said selected cell.
3. Mode of operation
The non-volatile counter used in the present invention carries out a counting operation by updating the data stored in the cell array having a predetermined bit number and forming an erasable and writable non-volatile memory device, based on count data.
Note, in the present invention, a cell corresponding to a value of the predetermined digit of said count from said cell array is selected by the selecting means and data corresponding to the value of a digit different from said predetermined digit is written in the selected cell by the writing means.
Namely, in the present invention, a plurality of cells are not simply provided in the non-volatile memory device for storing the count value but are arranged in a cell array, and thus a specific cell in the cell array can be designated by a value of a predetermined digit of the count value.
Therefore, the number of writing operations for writing data and the erasing operation for erasing same from each of the cells, can be reduced in proportion to the number of cells arranged in the cell array, and further, each cell can carry not only a value of a certain digit which the cell has memorized but also a value of a certain digit with respect to a position thereof in the cell array.
4. Effect of the Invention
According to the non-volatile counter used in this invention, cells comprising an array of a predetermined number of bits, constituting a volatile memory, are selected according to the predetermined digits of the count and data corresponding to the value of another digit is written in the cell, so the numbers of the erasing and writing operations per cell can be remarkably reduced at the lower digits of the conventional simple counter, and thus a superior and improved reliability of the count to be stored is obtained.
Further, each cell comprising the non-volatile memory carries not only information on the value of a certain digit stored by the cell but also information on the value of a predetermined digit obtained by the position of the cell in the array, so the volume of the information stored can be increased compared to the case wherein a plurality of cells is used.